Poration



Patented Aug. 28, 1928.

UNITED STATES- PATENT "o -rice.

A. PATRICK, OF BALTIMORE, MARYLAND, ASSIGNOR TO THE SILIOA' GEL COR- PORATION, OF BALTIMORE, MARYLAND, A CORPORATION 01! MARYLAND.

METHOD OF PREPARING STANNIC-OXIDE' GELS.

No Drawing. Original application filedFebruary 18; 1921, Serial No. 446,108. Dividednnd this applica-.

tion filed may 12, 1824. Serial No. 712,862.

The present application which is a division of my application 446,108 filed February 18, 1921, relates to a method of making an adsorbent and catalytic gelof stannic oxide.

In my Patent 1,297,724 for silica gel and process of making the same I disclosed and claimed a new method of producing hard porous highly adsorbent gels. The spe c1 fic example mentioned in the patent is silica gel.

Prior to my patent the only known way of producing gels employed the slow and impractical step "of dialysis. This was a laboratory method and would never have permitted the manufacture of gels in-such quantities and cheap enough, so that they could be employed in the arts. My patent above mentioned describes how to avoid this step and manufacture gels cheaply and uickly so that they can be utilized in many elds.

The present invention relates to another species of the invention disclosed in the patent. More specifically, it is directed to a method of producing the gel of staniiic oxide either as such or in combination with one or more of the oxides of aluminum, tungsten or titanium.

The principal object of the invention 18 to produce a gel of stamiic oxide either alone or combined with other colloidal oxides possessing great adsorbing powers, and by a method which is commercially practicable.

For the method of the present invention, I carefully determine the concentrations of an acid solution and a solution of a soluble salt, such as a sodium salt of the acid of stannic oxide, such that when mixed, will set to a hydrogel within four or five hours after mixing. Great care must be exercised" in bringing the acid and salt solutions'totion. Toprevent this coagulation it is necessary to vigorously stir the solutions at the moment of mixing. The amounts of the salt solution and the acid solution used are such as to give a. final concentration of the H ions coming from the acid in the mixture varying between one-tenth and five-tenths mols per litre. The salt solution should preferably be of a concentration of from 3% to 7%; by weight. 'Care should be taken to sodium stannate and acid solutions are thoroughly stirred at the time of mixing to prevent premature coagulation. The mixture sets to a hydrogel in a short time and is then broken into pieces and moisture removed as directed hereinafter.

e The temperature of the solutions during the time of mixin portant factor in t 6 time required for the setting of the hydrogel. At a temperature of about 50 C. the mixture sets to a hydrogel in thirty minutes to one hour-and the product 1s ust as good as the gel formed by mixing the solutions at 'a lower temperature but requiring a considerably longer time to set. Usually solutions at the time of mixing and at the time of setting are at atmospheric temperature but satisfactory results may be and setting is an imobtained at temperatures from 15 C. to 80 C. On mixing the acid and thesoluble salt solutions, a colloidal solution of the acid corresponding to the oxide is first formed. It is from this solution that the compound sets to a hydrogel. The hydrogel which is formed by allowing the mixture to set is then broken into ieces and washed free from acid and salt. 1? the wash water is heated this step is expedited. The washed hydrogel must now have its moisture removed to obtain the hard ge When this is effected by drying, it is essential that the water be removed slowly, as-the resulting finely porous condition of the gel obtained depends upon the proper dryin of the hydrogel. To this end the hydroge is first dried in a stream of air at 75 C. to 120C. After this heating the gel will still contain a considerable quantity of water and the greater part .of this is drivenofl byincreasing the temperature slowly up to 300 C; to 400 C. It may, however, be dried at 120 C. but this be said that not all the water s ould be i driven out of the gel.

will take longer. In a generalwa it may The resulting product is a most stable substance which ,can be safely heated to relatively high temperatures such as 700 Cuwithout fear of injury. The method of drying may be modifiedby taking the material after the first heating step as above described, and subjecting the same to a vacuum to further remove the water, the temperature during this vacuum treatment bein from 75 C. to 120 C. The product obtained by this method is just as stable as if the water had been removed by a further heating u to 300 C. to 400 C. The gel which is riiied in a vacuum is also stable to relatively high temperatures, such as 7 00 C. The final product is a hard, transparent substance ver closely resembling glass in appearance. en prepared in the above manner it is very orous, the pores being ultra-microspic an of exceedingl fine dimensions. It is because of this ne porous structure that the gel'is such an eflicient adsorbing medium. The hardness which the gel possesses is a desirable propertfor the reason that the gel will retain its s ape and structure and not crumble .or pack when placed in a vessel for the purpose of adsorb- 1n fluids.

that a solution of the sodium salt of the acid corre onding to the oxideis employed. It is to e understood, however, that any soluble salt of the acid corresponding to the oxide may be employed. The gel prepared in accordance with this invention, in addition to being an eflicient adsorbent of fluids, also possesses marked catalytic activity.

By mixing solutions of a soluble salt of the acid of stannic oxide and soluble salt of the acid of one or more of the oxides of aluminum, tungsten or titanium, a gel will be obtained which may be termed a plural oxide gel. The concentrations and quantities of the solutions are determined as al-' ready described, and the hydrogel formed by the mixture may have its moisture removed by drying as previously set forth. In this gen ions in the mixture have a concentration of one-tenth to five-tenths mols per litre.

Then the mixture is allowed to set to a hy- '1. In the process of preparing stanniccentration of the acid solution being such that the final concentration of the H ions resulting from the acid in the mixture is from one-tenth to five-tenths mols per litre.

2. In the process of preparing stannic oxide gel, the step of adding with thorough stiring, a soluble stannate to an acid, the amounts and concentrations of said solutions being such that the final concentration of H ions resulting from the acid in the mixture is from one-tenth to five-tenths mols per itre.

3. The process of reparing stannic oxide gel consistin in ad ing with thorough stirring a solub e stannate solution to an acid solution, said solution being of such concentrations and amounts that the final concentrations of H ions resulting from the acid in the mixture is from one-tenth to fivetenths mols per litre, whereupon after a time the mixture will set to a hydrogel without removal of an of the excess acid and salt, thereafter was ing said hydrogel to remove the acid and salt, and removing most of the v 7 water from the resulting product. the foregoing description it was stated nate to a solution of an acid, the concentration of the acid and the amounts of the solutions being such that the final concentration of H ions resulting from the acid in' the mixture is from one-tenth to five-tenths mols per litre, whereupon the mixture, after a time, sets to a hydrogel without removal of any of the excess acid and salt, washing the hydrogel to remove acid and salt, and removing most of the water from the resulting product. I

5. The process of reparing stannic oxide gel consisting in ad ing with thorough stir-' ring a soluble stannate solution to an acid solution, said solutions being of such amounts and concentrations that thefinal concentration of H ions resulting from acid in the mixture is from one-tenth to fivetenths mols per litre whereupon, after a time the mixture sets to a hydro el, washing said hydrogel to remove acid an salt, drying the hydrogel at a temperature of 75 to 120 C. to drive off a. part of the moisture and then slowly increase the temperature to drive off the greater part of the remainin moisture.

6. The process of preparin a p ural oxide gel containing stannic oxi e consisting in addin with thorough stirring solutions of a solu le stannate and soluble salts of the acids of the other oxides-to an acid solution, the solutions being of such concentrations and amounts that the final concentration of H ions resulting from the acid in the mixture is from one-tenth to five-tenths mols per litre, whereupon, after a time, the mixture will set to a hydrogel without removal of any of the excess acid and salts, washing to remove acid and salts and drying to remove most of the water from the resulting product.

7. A plural oxide gel being a hard glassy material having ultra-microscopic pores, stable in the presence of air up to high temperatures, and consisting of stannic oxide and one or more colloidal oxides.

8. In the process of preparing stannic oxide gel, the steps of allowing a colloidal solution of stannic acid to set to a hydrogel, dryin the hydrogel in a current of air heatec to 75 C. to 120 C. and then slowly increasing the temperature.

9. In the process of preparing stannic oxide gel. the steps of allowing a colloidal solution of stannic acid to set to a hydrogel, drying the hydrogel in a current of air heated to 75 to 120 C. and then slowly increasing the temperature to 300 to 400 C.

10. In the process of preparing stannic oxide gel the steps of allowing a colloidal stannic acid solution to set to a hydrogel, drying the hydrogel in a current of air heated to 75 to 120 C. and then slowly increasing the temperature to a point not exceeding 400 C.

11. In the process of preparing stannic oxide gel, the steps of allowing a colloidal solution of stannic acid to set to a hydrogel, dryin the hydrogel in a current of air heate to 75 to 120 C., subjecting the el tolalvacuum and then further heating t e ge 12. The process of preparing a plural oxide gel containing stannic oxide consisting in adding with thorough stirring 3% to 7% solutions of a soluble stannate and soluble salts of the acids of the other oxides to an acid solution, the solutions being of such concentrations and amounts that the final concentration of H ions resulting from the acid in the mixture is from one-tenth to five-tenths mols per litre, whereupon, after a time, the mixture will set to a hydrogel without removal of any of the excess acid and salts, washing to remove acid and salts and drying to remove most of the water from the resulting product. a

In testimony whereof I hereunto aflix my signature.

WALTER A. PATRICK. 

